This invention relates to an automatic diluter and more particularly to a diluter which permits precise dilution of sample fluids with repeatable accuracy.
Laboratory test equipment for performing qualitative or quantitative analyses on fluids, such as blood cell counts or hemoglobinometry on blood samples, require dilution of the sample fluids in ratios on the order of 101:1 to 500:1 or higher, accurate to precise tolerances, in order to insure accuracy of test results. Automatic diluters, which replace tedious manual dilution procedures, are well known in the prior art. U.S. Pat. Nos. 3,690,833; 3,764,268 and 3,982,667 illustrate examples of previously known automatic units. However, to deliver the precise dilution required, typical prior art diluters were dependent on the ability to control both the volume of the sample fluid and the correspondingly large volume of diluent at the moment of their initial injection into the apparatus. Possible volumetric errors inherent in the particular injection mechanism utilized could affect each of the independently injected quantities of fluids, resulting in a cumulatively large deviation from the desired dilution ratio. So, if calibration and operator errors are also taken into consideration, diluters based on such an operating principle would have four major sources of error inherently built in.
Another variable having an adverse effect on dilution accuracy is the presence of residual amounts of sample fluid in the diluter's sample inlet line, which can contaminate the particular sample being processed. Typically, prior sampler/ diluters would have to perform a specific step in the operation directed solely to cleaning such residue from the system. U.S. Pat. No. 3,719,086 is illustrative of this approach.
An object of the present invention is to provide an automatic diluter which will deliver a constant volume of sample for dilution by a simple, inexpensive mechanism, free from cyclic volumetric errors and relatively immune to loss of accuracy with the passage of time.
Another object of the invention is to provide an automatic diluter which is simple to set up and adjust to yield accurate dilution ratios, and which presents fewer opportunities for operator error.
Still another object of the invention is to provide an automatic diluter which will remove sample residue from the sample inlet as a necessary consequence of the normal sample intake procedure and eliminate any superfluous intermediate cleaning step.